This invention relates to a process for the preparation of diphenylamine from aniline in the liquid phase, in the presence of boron/fluorine compounds and water.
A process for the preparation of diphenylamine by heating aniline with small amounts of boron fluoride, or of an aniline/boron fluoride or ammonia/boron fluoride complex, under pressure to temperatures between 250.degree. and 400.degree. C is described in German Published Specification No. 1,116,231. However, with this process the reaction must be carried out with anhydrous aniline and, in addition, recovery of the catalyst involves considerable effort.
Furthermore, a process for the preparation of diphenylamine by heating aniline under elevated pressure in the presence of boron fluoride as the catalyst is known from U.S. Pat. No. 3,071,619 and in the process boron fluoride is preferably employed as ammonium fluoborate. The disadvantage of this process lies in the insolubility of the solid catalyst, that is to say ammonium fluoborate, in the reaction mixture and the metering and separating problems associated therewith.